CT430 - Soft Starters on Motor Applications · Simplest Starting Solution Full torque applied…motor Mechanical wear ≥6x inrush current Soft Start Simple Starting and Stopping

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Copyright © 2018 Rockwell Automation, Inc. All Rights Reserved. 1

CT430 - Soft Starters on Motor Applications

Bill Bernhardt

Sr. Commercial Engineer

May 16, 2018

PUBLIC Copyright © 2018 Rockwell Automation, Inc. All Rights Reserved. 2

Topics

Additional Resources

Applications

Motor Characteristic Information

Soft Starter Methods

Traditional Motor Starting Methods


Topics


Applications





Reasons for Soft Motor Starting

• Minimize mechanical damage of system components and product

• Belts, Gears, Drive Shafts and Keyways

• Reduced Product Spillage

• Water Hammer and Mechanical Vibration

• Better Energy “Management”

• Limit in-rush current

– Optimize the size of transformers / generators / switch gear

• Meet Power Company Requirements / Rebate programs

• Manage Control under Power Distribution Limitations

• Energy Cost Reduction (Peak Demand Charges)


Selection Process

1. What is the application?

Conveyor

High Inertia

Pump

Shock Load

2. What motor to select?

Motor to handle the load

Handle long start times if high inertial loads

If possible, know the power source

3. What starting method to choose?


Full Voltage (DOL)

Simplest Starting Solution

Full torque applied…motor

Mechanical wear

≥6x inrush current

Soft Start

Simple Starting and Stopping

Limited Control at various

speeds

Reduced torque and current

during starting

Motor Starting Methods

Basic Advanced

3

SCPD

Optional

Isolation

Contactor

SMC

M3

SCPD

VFD

M

AC / DC / AC

Converter

3

SCPD

Contactor

M

Overload

DOL

VFD (AC Drive)

Complete Continuous Control

at any Speed

Full torque at any speed

without sacrificing current

No Starting Choices Up to 17 different starting/stopping modes

Unlimited starting possibilities when sized properly

3

SCPD

Optional

Isolation

Contactor

SMC

M3

SCPD

VFD

M

AC / DC / AC

Converter

3

SCPD

Contactor

M

Overload

DOL

3

SCPD

Optional

Isolation

Contactor

SMC

M3

SCPD

VFD

M

AC / DC / AC

Converter

3

SCPD

Contactor

M

Overload

DOL


Motor Starting Methods

VFD (AC Drive)

Complete Continuous Control

at any Speed

Full torque at any speed

without sacrificing current

Highly efficient motor and

application performance

More complex setup and install

Larger footprint

Impact on Power Quality

EMC remediation

Application Considerations

Motors types

Lead Lengths

Wire Type

Ambient Conditions

Soft Start

Simple Starting and Stopping

Limited Control at various speeds

Reduced torque and current

during starting

Simple…adjust and setup

Reduced installation costs

Smaller footprint

None to minimal need for

harmonic/EMC mitigation

Highly efficient when running at

full speed

Energy Saver Performance for

light loads

Unlimited starting possibilities when sized properly

Up to 17 different starting/stopping modes

Full Voltage (DOL)

Simplest Starting Solution

Full torque applied…motor

Mechanical wear

≥6x inrush current

Peak demand charges

Limited functionality

Unless used with

advanced Overload

Finite Mechanical Life

Contacts will wear out

No Starting Choices


How does Full Voltage (DOL) work?

Full voltage, current and torque applied immediately

Power is immediately removed when shut off

Full Voltage (DOL)

3

SCPD

Optional

Isolation

Contactor

SMC

M3

SCPD

VFD

M

AC / DC / AC

Converter

3

SCPD

Contactor

M

Overload

DOL High starting torque can cause damage

to mechanical system

High current can cause problems in the electrical system

and can also cause decreased system capacity


A VFD converts AC line voltage to DC voltage and then inverts it back to a

pulsed DC whose RMS value simulates an AC voltage.

Most VFDs utilize a full wave diode-bridge or SCR rectifier bridge to convert

the AC line to DC voltage (DC bus).

Many VFDs have DC inductors to improve power factor and reduce

harmonics.

Typically Insulated Gate Bipolar Transistors (IGBTs) are used to invert the

DC Bus voltage.

VFD (AC Drive)

How does an AC Drive work?


Most common VFDs manufactured utilize pulse width modulation (PWM) to

create the output sine wave.

During acceleration, the inverter applies different frequencies to the motor.

It also changes the voltage in proportion to the frequency. (unlike SMCs)

The inverter produces rated torque from 0 to rated speed. (unlike SMCs)

Inverter output can be any frequency below or above the line frequency --

up to the limits of the inverter or mechanical system. (unlike SMCs)

VFD (AC Drive)

How does an AC Drive work?


3 pairs of back-to-back Silicon-Controlled Rectifiers (SCRs) are used to start and stop the motor.

SCRS only, NO AC Front End, NO DC Bus, NO IGBTs

Back-to-back orientation of SCRs allow control of AC line every half cycle

Regulates voltage from 0 volts up to line voltage. Line frequency is not controlled.

Soft Start (SMC)

How does a Soft Starter work?


Voltage controls the current and torque.

The % change in motor torque is approximately proportional to the square

of the % change in applied voltage.

Current is directly related to the voltage applied to the motor

Voltage is ramped up to full voltage or limited to provide current limited starts

Line frequency (50 /60Hz) is always applied to the motor.

Soft Start (SMC)



Topics


Applications





How do these methods work?


100%0

Speed -RPM

To

rqu

e

(ftl

b)100%

72%

25%

600%

510%

300%

100% Voltage85% Voltage50% Voltage

Full Load

Torque required by the load

%F

LA

(am

ps)

Current

Torque

How do these methods work?SMC Soft Start



Full Voltage Not a common Starting mode.

NOTE: Full voltage required to accelerate the

motor may be a sign of other problems (i.e.

Initial Torque of > 90%)

Used as a Solid State Contactor for High cycle

rates

Soft Starter Modes of Operation



Soft Start Primarily used to limit mechanical stress

Constant or exponentially increasing load

(Compressors, Pumps, Conveyors)

Soft Start/Current Limit

with Kick Start Kick Start is needed to overcome static condition

Example when used:

Cold system components

Loaded conveyor



Current Limit Primarily used to limit line disturbances

Constant or very lightly loaded motor

Good on high inertia applications

(Bandmills, Fans, Centrifuge, Ball Mill, Washers)

Pump Control Legacy version of torque control

optimized for centrifugal loads

Simple to apply but some considerations

Exponentially increasing load such as Compressors, Pumps, Conveyors



“Patented” Sensor-less Linear Acceleration Starting Mode

Accomplished via Advanced Motor Speed Estimation Algorithm

– No external feedback required - reduces cost and potential for failure

– Provides exacting motor acceleration control under varying load conditions

Simple to set up

– 2 parameters required to configure: Ramp Time and Initial Torque

(used as reference)

– Reduces/eliminates the need for the Dual Ramp mode

Always uses the minimum amount of energy needed to accelerate the motor in the time requested

(regardless of the loading condition)

Sensorless Linear Acceleration (Linear Speed) Starting Mode:


Stopping Modes of Operation

Soft Stop Reduces voltage to stop

Longer than coast

Good for gradually stopping a motor

Motor Braking Internal or external means

Stops motor faster than coast

Saves time for maintenance of

equipment.


Soft Starter: Choosing a Power Platform

Internal Bypass

Ideal for small spaces

Smallest total footprint

Easy selection and application

Lowest total installed cost

Solid State

Ideal for critical performance in tough

environmental conditions

Allows for Specialized Control

External Bypass offers operational flexibility

and redundancy

21

Hybrid Power Structure Solid State Power Structure


Soft Starter Bypass

Internal Bypass Typically IEC rated

Smaller over all foot print

Soft start operates cooler

External Bypass Choice of contactor

Good for rough environments

If the control wiring is correct, can also

be utilized as emergency bypass


Topics


Applications





Are All Motors the Same?






Basic Information

Ask for a speed torque curve of the SMC


Basic Information

Ask for motor information

Table 430.7(B) of NEC for locked-rotor indicating code letters.


Basic Motor Information

Motor Code Letter

Table 430.7(B) of NEC for locked-rotor indicating code letters.


Basic Information


Motor Nameplate


Topics


Applications





Application Examples


Pump Control

Water hammer prevention/reduction

Soft start / stop method for soft power situations

Pump control follows the pump S-curve

Linear acceleration/deceleration


Fan

Variable torque load

Start with closed dampers

Soft start ramps the voltage



Conveyor

Constant torque application

Soft start / stop common starting


Reduce shock to the system


High Inertia Loads

Long starts for large mass

Current limit method is common

Coast or some kind of braking stop

Heat generation


Wye-Delta Starters

Open Transition

Closed Transition

3

Two types of Wye-Delta starters


Wiring the Soft Starter Inside the Delta

3

Two connections scenarios with the soft starters

Inside-The-Delta Line


Slow Speed

Slow Speed – Common:


Slow Speed

SMC-50 Enhanced Slow Speed:


Understand the System Dynamics High inertia applications

No load/Light Load (Good applications)

Fan, centrifugal pump, conveyors, Compressors

Full load (Not recommended)

Extruders, positive displacement pumps, Inclined Conveyors (Overhauling load), Lifts,

Elevators (unless hydraulic)

Retro-fit applications

Motor may have been designed for full voltage only

Not a replacement for a mechanical device (Clutch)




Power Source Sizing Guidelines

Ideally, the source would be sized for a full voltage start. (Somewhat impractical today)

When sizing for use with a Generator it is critical that the generator is able to stay in proper regulation under starting or braking loads.

Rule of thumb: Avoid sizing the supply for anything less the 300% of the motors FLA.

SCR Fusing (Very Fast Acting Semiconductor type)

Protect SCRs, not typically rated for branch circuit protection

Use is not suggested in High Inertia, Braking, or Pump stop applications (Applications with Start times > 30 seconds)


“Rules of Thumb”

For Soft Starter applications, some general guidelines include:

Full speed operation

Reduction of mechanical wear and damage to system

Lightly or moderately loaded applications

Lower starting torque applications

Limiting current is prime reason for starting method


Application, Application, Application!

Selection guides are correct for 90% of applications.

Simply choose based on voltage, horsepower, and insure that the motor FLA fits the products operating range

10% of applications require a closer look.

In applications where the actual run current is less the 40% of the FLA, choose the current range that best fits the nominal running current without exceeding the HP range for the product.

Thermal Analysis may be required to determine proper size for the following:

Extended starting times

Aggressive Duty Cycle (> 10 times/hr)

Operation in elevated ambient temperatures

LRA > 600% (i.e. High efficiency motors, Design A)



Problem: A towline conveyor at the end of a production

line had frequent damage to the gearbox caused by the

starting torque from across-the-line starting of the

motor. There were also frequent spills during starting

and stopping. Occasionally, the conveyor needed to be

started under heavy load. This towline application had a

variety of starting requirements that other soft starters

could not satisfy. Investing in a variable speed drive was

not cost effective.



Problem: A centrifuge required a reduced voltage start because

of power company restrictions. The high torque during starting

was causing damage to the gearbox. A shorter stopping time

than the present fifteen minute coast-to-rest was desired. The

long stop time caused delays in the production process. A Wye-

Delta starter with a mechanical brake was currently in use. A

zero speed switch was used to release the brake. The

mechanical brake required frequent maintenance and

replacement, which was costly and time consuming. Both the

mechanical brake and zero speed switches were worn out and

required replacement.



Problem: Because of the remote location of

the facility and power distribution

limitations, a reduced voltage starter was

needed on a bandsaw application. The saw

was turned off only during shift changes.

When the saw blade became dull, the

current drawn by the motor increased.

Therefore, an ammeter was required.

Metering the application for jam conditions

was a necessity. In addition, single phasing of

the motor was a problem because of

distribution limitations.



Problem: A bandsaw required 25 minutes to

coast to a stop to routinely change the saw

blade. A braking package was required to

reduce the stopping time. Other methods

using dedicated braking devices were

investigated but were unacceptable because

of overly complex installation. These methods

required additional panel space for the brake

module, brake contactors, and timers.

Because of potential alignment problems, it

was dangerous to bring the saw up to full

speed after installing a new blade.


Topics


Applications





SMC Family Brochure

Whitepapers

Blogs

Tech Data Documents

https://www.rockwellautomation.com/global/literature-library/overview.page

https://www.rockwellautomation.com/global/news/blog/overview.page


https://www.rockwellautomation.com/global/literature-library/overview.page

https://www.rockwellautomation.com/global/news/blog/overview.page


Wizards

https://ab.rockwellautomation.com/motor-control/lv-soft-starters/smc-50#resources

https://ab.rockwellautomation.com/motor-control/lv-soft-starters/smc-50#resources


Before Getting Into Starting Method

1. What is the application?

Conveyor

High Inertia

Pump

Shock Load

2. What motor to select?

Motor to handle the load

Handle long start times if high inertial loads

If possible, know the power source

3. What starting method to choose?


Questions???


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Copyright © 2017 Rockwell Automation, Inc. All Rights Reserved. 56

Soft Starters on Motor Applications